Method for forming an intermittent stream of particles for application to a fibrous web

ABSTRACT

The present invention provides a method and apparatus for applying discrete particles of absorbent material to a predetermined location on a fibrous web. The apparatus comprises a continuously rotating mask, and a means for directing a supply stream of absorbent particles to form an acute included angle with a diverting surface on the rotating mask. The mask diverting surface splits the supply stream of absorbent particles into a first intermittent stream passing through the mask and a second intermittent stream deflected by the diverting surface. The absorbent particles in one of the first and second intermittent streams is directed to the fibrous web.

This is a divisional of application Ser. No. 08/139,249, filed on Oct.19, 1993, now abandoned.

FIELD OF THE INVENTION

This invention is related to a method and apparatus for forming fibrouswebs having a predetermined distribution of particulate material. Moreparticularly, the invention is related to forming an intermittent streamof particulate material for application to a fibrous web.

BACKGROUND OF THE INVENTION

Absorbent articles such as disposable diapers, incontinence pads, andcatamenial napkins generally include an absorbent core for receiving andholding body exudates. The absorbent core typically includes a fibrousweb, which can be a nonwoven, airlaid web of natural or syntheticfibers. A class of particulate absorbent materials known assuperabsorbent polymers or absorbent gelling materials can beincorporated in the fibrous web to improve the absorption and retentioncharacteristics of the fibrous web.

Because absorbent gelling materials are generally significantly moreexpensive than readily available natural or synthetic fiber materials(e.g., cellulose fibers), it is advantageous to reduce the quantity ofabsorbent gelling material in the core. Rather than uniformly reducingsuch particles throughout the entire core, it is desirable to distributethe particles in the absorbent core in a predetermined manner so thatthe particles are located where they will be most effective in acquiringand retaining body exudates.

Various techniques have been developed to distribute and locateabsorbent materials on or within a fibrous substrate. U.S. Pat. No.4,800,102 issued to Takada discloses applying a powder to the topsurface of a substrate by spraying powder through an opening in arotating disc member. Powder not passing through the opening is shown tobe supported on a horizontal surface of the disc as the disc rotates,and is subsequently scraped from the disc by a scraper into a receivingmember below the scraper. Powder not removed by the scraper is removedby a vacuum sucker positioned above the disc. Such an arrangement isdisadvantageous because it requires powder material to accumulate on thedisc. The arrangement requires a relatively complicated scraper andvacuum device to remove powder from the disc. Centrifugal forces maycause some of the accumulated powder to be flung from the disc, therebycomplicating powder recycling. Powder accumulating on the disc prior toremoval may also cause rotary imbalance and vibration of the disc,especially if the disc is rotated at the relatively high speedsdesirable for cost effective production rates. Further, the powdermaterial is shown to be directed generally perpendicular to the discsurface. Therefore, powder material may strike and bounce off of thedisc in an unpredictable direction, thereby further complicating powderrecycling.

U.S. Pat. No. 5,028,224 issued to Pieper et al. discloses pulsing anddiverting mechanisms for producing an intermittent flow of absorbentparticles. The diverting mechanism includes a flap which rotates about apivot between a closed position and an open position to provide anintermittent quantity of particulate material. Such an arrangement isundesirable because operation of such a flap between the open and closedpositions requires accelerating and decelerating the flap between twostationary positions. Operating such a reversing mechanism at highspeeds can result in undesirable inertial forces in the mechanism, andcomplicates precise control of the definition of the pulse of theparticulate material.

U.S. Pat. No. 5,213,817 issued to Pelley discloses a stream of powdermaterial passing through a nozzle which is movable between first andsecond positions. A flow separator splits the stream into twointermittent streams as the nozzle is moved between the first and secondpositions. As in Pieper et al. above, such an arrangement is undesirablebecause operation of the nozzle between two positions requiresaccelerating and decelerating the nozzle between two stationarypositions. Reversing the direction of motion of the nozzle at highspeeds results in undesirable inertial forces, and complicates precisecontrol of the definition of the pulse of particulate material.

Accordingly, it is an object of the present invention to provide anapparatus and method for applying discrete particles to a fibrous web.It is another object of the present invention to provide a pulse ofdiscrete particles for application to a predetermined location on afibrous web. Another object of the present invention is to provide acontinuously rotating mask having a particle diverting surface formingan acute included angle with a supply stream of particles to split thestream of discrete particles into a first intermittent stream passingthrough the mask and a second intermittent stream deflected by thediverting surface.

SUMMARY OF THE INVENTION

The present invention comprises an apparatus for and method of applyingdiscrete particles to a predetermined location on a fibrous web. Theapparatus includes a conveyor for supporting and moving the fibrous web;a means for forming a supply stream of discrete particles; a mask movingcontinuously relative to the supply stream of particles; a divertingsurface on the mask for splitting the supply stream of particles into afirst intermittent stream passing through the mask and a secondintermittent stream deflected by the diverting surface; a means fordirecting the supply stream of discrete particles to form an acuteincluded angle with mask diverting surface; and a means for directingthe discrete particles in one of the intermittent streams of particlesto the fibrous web.

The apparatus can include a foraminous forming element for forming anairlaid fibrous web; means for forming an air-entrained flow of fibers;means for combining the flow of fibers with one of the first and secondintermittent streams to form a combined stream comprising anintermittent stream of particles within a continuous stream of fibers;and means for directing the combined stream of fibers and particles tothe forming element. In a preferred embodiment, the mask is supportedfor continuous rotation about an axis, and the supply stream of discreteparticles forms an included angle of less than 45 degrees with thediverting surface.

The method preferably comprises the steps of:

a. providing an airlaying means having a foraminous forming element forforming a fibrous web;

b. providing an air-entrained stream of fibers;

c. providing an air-entrained supply stream of discrete particles;

d. providing a mask having a diverting surface;

e. continuously rotating the mask about an axis;

f. directing the supply stream of discrete particles to form an acuteincluded angle with the diverting surface for splitting the stream ofdiscrete particles into a first intermittent stream of particles passingthrough the mask and a second intermittent stream of particles deflectedby the diverting surface;

g. combining the stream of fibers with one of the intermittent streamsof particles to form a combined stream comprising an intermittent streamof particles within a continuous stream of fibers; and

h. directing the combined stream of fibers and particles to the formingelement of the airlaying means.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the present invention, it is believed thepresent invention will be better understood from the followingdescription in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an absorbent article shown partiallycut-away.

FIG. 2 is a cross-sectional view of an absorbent core having a dustinglayer and a layer including discrete particles of absorbent material.

FIG. 3 is a schematic illustration of an apparatus according to oneembodiment of the present invention having one particle recyclingarrangement.

FIG. 4 is a schematic illustration of an apparatus according to analternate embodiment of the present invention having an alternativeparticle recycling arrangement.

FIG. 5 is a cross-sectional side view of the mask supported in anenclosure and the mask delivery nozzle.

FIG. 6 is a view taken along line 6--6 in FIG. 5 showing the masksupported in the enclosure, with the enclosure partially cut-away.

FIG. 7 is a plan view of a mask having apertures in the divertingsurface.

FIG. 8 is a schematic illustration of a longitudinal distribution ofparticulate material in an absorbent core.

FIG. 9 is a plan view of a mask having apertures with different radialwidths for forming a lateral distribution of particles shown in FIG. 11.

FIG. 10 is a schematic illustration of a means for providing phasing ofthe position of the mask with the position of the foraminous formingelement.

FIG. 11 is a schematic illustration of a lateral distribution ofparticulate material in an absorbent core.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention will be described in the context ofproviding airlaid fibrous webs for use as absorbent cores in disposableabsorbent articles such as disposable diapers, the present invention mayalso be employed to provide absorbent webs for use in a number of otherarticles, including but not limited to incontinence briefs, disposabletraining pants, and sanitary napkins.

FIG. 1 shows a disposable diaper 20 having a liquid pervious topsheet22, a liquid impervious backsheet 24, and an absorbent core 26 disposedbetween the topsheet 22 and the backsheet 24. Preferred constructions ofsuch disposable diapers are described in U.S. Pat. No. 3,860,003 issuedJan. 14, 1975 to Buell and U.S. Pat. No. 5,151,092 issued Sep. 29, 1992to Buell et al., which patents are incorporated herein by reference. Thediaper 20 has a longitudinal centerline 21 and a lateral centerline 23.As used herein, the "longitudinal" dimension, direction, or axis of thediaper 20 is aligned front to back with respect to the wearer as thedisposable absorbent article is worn. The "lateral" dimension,direction, or axis of the diaper 20 is perpendicular to the longitudinaldirection and is sideways aligned as the diaper is worn.

The absorbent core 26 can include two or more components, such as afirst insert core component 32 and a second shaped core component 34.Preferred absorbent core constructions are described in U.S. Pat. No.4,673,402 issued Jun. 16, 1987 to Weisman et al.; U.S. Pat. No.4,685,915 issued Aug. 11, 1987 to Hasse et al.; U.S. Pat. No. 4,834,735issued May 30, 1989 to Alemany et al.; U.S. Pat. No. 5,217,445 issuedJun. 8, 1993 to Cook et al.; and U.S. Pat. No. 5,234,423 issued Aug. 10,1993 to Alemany et al., which patents are incorporated herein byreference. The insert core component 32 serves to collect and distributedischarged body fluid, and can comprise a web of hydrophilic fibermaterial. The insert core component 32 can be free of particles ofabsorbent gelling material, or alternatively, can include an amount ofparticles of such material.

The shaped core component 34 absorbs discharged body fluids from theinsert core component 32 and retains such fluids. As shown in FIGS. 1and 2, the shaped core component 34 includes a thin dusting layer 35 ofhydrophilic fiber material overlayed by a primary layer 36 of acombination of hydrophilic fiber material and discrete particles 38 ofsubstantially water insoluble, fluid absorbing, absorbent gellingmaterials. While the dusting layer 35 is preferably a relatively thinlayer of hydrophilic fiber material, it should be understood that theterm "dusting layer" denotes a layer of the fibrous web and includeslayers having any thickness.

There are several suitable absorbent gelling materials which can be usedto form the discrete particles 38 in the shaped core component 34, suchas silica gels or organic compounds such as crosslinked polymers.Particularly preferred absorbent gelling materials are hydrolyzedacrylonitrile grafted starch, acrylic acid grafted starch, polyacrylatesand isobutylene maleic anhydride copolymers, or mixtures thereof. U.S.Pat. Re 32,649 reissued to Brandt et al. Apr. 19, 1988 is incorporatedherein by reference for the purpose of showing suitable absorbentgelling materials.

FIG. 3 shows an apparatus according to the present invention for formingan intermittent stream of absorbent gelling material particles andapplying the intermittent stream of materials to a fibrous web. Anintermittent stream of particles is a stream of particles having aparticle flow rate which is periodically stopped or reduced. Theapparatus includes a conveyor for supporting and moving a fibrous web,and preferably comprises an airlaying means such as a rotating drum-typeairlaying module 40 having a foraminous forming element, such as aforaminous forming drum 42. Airlaying module 40 is suitable for formingan airlaid fibrous web 41, such as shaped core component 34.

The apparatus also preferably includes a means for forming anair-entrained stream of fibers 62, such as a disintegrator 70. Theapparatus further includes a means for forming a supply stream 82 ofdiscrete absorbent gelling material particles 38 such as a particlemetering device 80 and an eductor 90.

The apparatus according to the present invention includes a mask 100continuously moving with respect to the supply stream 82 of discreteparticles. In a preferred embodiment the mask 100 is continuouslyrotated about an axis 101. The mask can be rotated about axis 101 by anysuitable means, such as by a motor 104 and shaft 102 shown in FIG. 3.The mask 100 includes a diverting surface 110 for splitting the supplystream 82 of discrete particles into a first intermittent stream 103 ofparticles passing through the mask 100 and a second intermittent stream105 of particles deflected by the diverting surface 110.

The apparatus according to the present invention also includes a meansfor directing the supply stream 82 of discrete particles to form anacute included angle A (FIG. 5) with the diverting surface 110. Themeans for directing the supply stream 82 to form an acute included angleA with the diverting surface 110 can include a mask delivery nozzle 120,shown in FIGS. 3, 4, 5, and 6. The apparatus can further include a meansfor combining the stream of fibers 62 with the first intermittent stream103, such as a diverging duct 65, to form a combined stream 66comprising an intermittent stream of particles within a continuousstream of fibers. A means for directing the combined stream 66, such asa drum hood 50, directs the combined stream 66 to the foraminous formingelement 42 of the airlaying apparatus 40.

Referring to the components in FIG. 3 in more detail, the disintegrator70 can include a rotary element 74 enclosed in a housing 72. Thedisintegrator 70 receives a fibrous sheet material 71 capable of beingseparated into individual fibers. The fibrous sheet material 71 caninclude synthetic and/or natural fibers, and preferably comprisescellulosic fibers. The rotary element 74 can be continuously driven inthe direction shown in FIG. 3. Teeth on the rotary element 74 separatethe individual fibers of the sheet material 71 as the sheet material 71is fed into the disintegrator 70.

The disintegrator 70 can include splitter chute 76 for forming multiplestreams of air-entrained fibers from the individual fibers separated bythe rotary element 74. The splitter chute 76 can be directly orindirectly joined to or disposed within the housing 70. The splitterchute 76 provides the air-entrained stream of fibers 62, as well as adusting layer air-entrained steam of fibers 63 for forming the dustinglayer 35 shown in FIG. 2. The air-entrained stream of fibers 62 iscarried from the splitter chute 76 by conduit 60, and the dusting layerair-entrained stream of fibers 63 is carried from the splitter chute 76by dusting layer conduit 67.

U.S. Pat. Nos. 4,908,175 and 4,765,780, issued Mar. 13, 1990 and Aug.23, 1988, respectively, to Angstadt et al., are incorporated herein byreference for the purpose of showing the construction of a suitabledisintegrator 70 and splitter chute 76 for providing the air-entrainedstream of fibers 62 and the dusting layer air-entrained stream of fibers63. However, it will be understood by those skilled in the art thatother apparatus for separating a roll or mat of fibrous material intoindividual fibers, including but not limited to hammermills, fiberizers,picker rolls, and lickerin rolls, may be used to provide theair-entrained streams of fibers 62 and 63.

The airlaying module 40 includes the rotating foraminous forming drum 42on which the fibrous webs 41 can be formed. The foraminous forming drum42 can include a plurality of formation cavities 44 circumferentiallyspaced about the periphery of the forming drum 42. Five formationcavities 44 are shown in FIG. 3, with each formation cavity 44 having acircumferential span of about seventy-two degrees. The forming drum 42is rotated by a motor 45 (FIG. 10) or other suitable device. The formingdrum 42 rotates in the direction shown in FIG. 3 such that fibers in thedusting layer air-entrained stream of fibers 63 are first deposited inthe formation cavities 44 to form the dusting layer 35 shown in FIG. 2.The combined stream 66 is then deposited in cavities 44 to overlay thedusting layer and form the primary layer 36 comprising a combination ofhydrophilic fiber material and discrete particles of absorbent gellingmaterials.

The airlaying module 40 includes a plurality of vacuum chambers (notshown) within the interior of the foraminous forming drum 42. Each ofthe vacuum chambers is connected to a suitable source of vacuum (notshown). Entrainment air for forming air-entrained streams of fibers 62and 63 is drawn through the foraminous forming drum 42 by the vacuummaintained in the vacuum chambers within the interior of the formingdrum 42. U.S. Pat. No. 4,592,708 issued Jun. 3, 1986 to Feist et al. andabove referenced U.S. Pat. Nos. 4,908,175 and 4,765,780 are incorporatedherein by reference for the purpose of showing a suitable airlayingmodule 40 for use with the present invention.

FIG. 3 shows one embodiment of the present invention. Discrete particles38 of absorbent gelling material are directed from a supply source (notshown) to branched conduit 307 as indicated by arrow 305. A valveassociated with branched conduit 307 is movable from a first position309A to a second position 309B shown in phantom.

In a first operating mode the valve is positioned in the first position309A so that the discrete particles 38 of absorbent gelling material aredirected to and accumulated in a filter receiver vessel 300. Air infilter receiver vessel 300 is removed through a filter 330 and airconduit 320 by a suitable vacuum source 340.

The particles in filter receiver vessel 300 are gravity fed to theparticle metering device 80. The metering device 80 delivers apredetermined mass of discrete particles 38 per unit time. The meteringdevice 80 can include a hopper 84, screw feeder 86, and scale 88. Asuitable metering device is an Acrison Volumetric Feeder, Model No.405-105X-F, available from Acrison, Inc. of Moonachie, N.J.

The metered quantity of particles 38 is delivered by screw feeder 86 toa funnel receiver 91 and directed to an eductor 90. Eductor 90 entrainsthe metered quantity of particles 38 within a motive air flow to providethe air-entrained supply stream 82 of discrete particles. The motive airflow can be provided by a suitable blower 92. A suitable eductor 90 is aFox Eductor, Model No. 612046, available from the Fox Valve DevelopmentCorporation, of Dover, N.J. A suitable blower 92 is a Fuji Blower, ModelVFC503A, available from the Fuji Electric Corporation of America,Lincoln Park, N.J.

The air-entrained supply stream 82 of discrete particles is carried by aparticle carrying conduit, which can comprise a particle delivery chute94 and the delivery nozzle 120. The delivery chute 94 carries the supplystream 82 of discrete particles to the mask delivery nozzle 120. Themask delivery nozzle 120 directs the supply stream 82 to form an acuteincluded angle A with the diverting surface 110 of the mask 100. Theparticles 38 in the first intermittent stream 103 passing through themask 100 are combined with the air-entrained stream of fibers 62 in thediverging duct 65, and directed to the foraminous forming drum 42 by thehood 50.

The particles 38 in the second intermittent stream 105 are deflected bythe diverting surface 110 of the mask 100. The momentum of the particlesin the second intermittent stream 105 carries the particles in apredetermined direction (vertically downward in FIG. 3) to enter aconduit 410. The deflected particles are carried in the conduit 410 forrecycling. In the embodiment shown in FIG. 3, the conduit 410 carriesthe diverted particles to vacuum receiving chamber 400. A vacuum source450 provides an airflow through a particle filter 430 for drawing theparticles in conduit 410 into the vacuum receiving chamber 400. Asuitable vacuum source 450 is commercially available from the BuffaloForge Company of Buffalo, N.Y. as Model No. 3RE.

The recycled particles accumulate in the vacuum receiving chamber 400during the first operating mode. In a second operating mode, the valveassociated with branched conduit 307 is moved to position 309B, therebyblocking the flow 305 of discrete particles from the supply source. Withthe valve in position 309B, a rotary air lock 420 positioned under thevacuum receiving chamber 400 is rotated to gravity feed at least aportion of the accumulated recycled particles in chamber 400 into apick-up pan 490. The rotary air lock 420 permits the accumulatedrecycled particles in chamber 400 to enter the pick-up pan 490, whilemaintaining the vacuum in chamber 400 provided by the vacuum source 450.A suitable rotary air lock 420 is available from Prater Industries, Inc.of Chicago, Ill. as Model No. PAV-6C. A blower 492 is activated toprovide a motive air flow for carrying the recycled particles enteringpick-up pan 490 through a conduit 493. The recycled particles carried inconduit 493 pass through branched conduit 307 and into the filterreceiver vessel 300.

The apparatus is returned to the first operating mode by deactivatingthe rotary air-lock 420 and the blower 492, and by moving the valveassociated with the branched conduit 307 to position 309A. Thetransition between the first and second operating modes can be made at apredetermined time-interval, or alternatively, can be made based on theamount of recycled particles accumulated in the chamber 400.

FIG. 4 shows an alternative embodiment of the present invention forproviding an air-entrained stream 82 of discrete particles and recyclingthe second intermittent stream 105 of particles not combined with theair-entrained stream of fibers 62. Discrete particles 38 of absorbentgelling material are carried by a conduit 310 from a supply source (notshown) to a filter receiver vessel 300 as indicated by arrow 305. Avacuum source 340 provides a motive air flow through a particle filter330 and a conduit 320 for carrying the discrete particles into thevessel 300.

The particles in filter receiver vessel 300 are gravity fed to theparticle metering device 80. The metering device 80 delivers apredetermined mass of discrete particles per unit time. The meteringdevice 80 can include a hopper 84, screw feeder 86, and scale 88 asdescribed above with reference to FIG. 3. The metered quantity ofparticles is delivered by screw feeder 86 to a finnel receiver 91 andcarried by a conduit 93. The conduit 93 empties the metered quantity ofdiscrete particles into the conduit 410, so that the metered quantity ofdiscrete particles is combined with the second intermittent stream 105of particles deflected by the mask 100. Both the conduit 93 and theconduit 410 can be inclined vertically downward to provide gravityassisted feeding of the metered quantity of particles and the detectedparticles. The combined stream of metered and defected particles isindicated by arrow 412 in FIG. 4.

The conduit 410 directs the combined stream of particles 412 to aneductor 90. The eductor 90 and a blower 92 entrain the combined streamof particles 412 within a motive air flow to provide the air-entrainedsupply stream 82 of discrete particles. A suitable eductor 90 is a FoxEductor, Model No. 300-SCE-SS available from the Fox Valve DevelopmentCorporation. A suitable blower 92 is a Cooper/Sutorbilt Blower, Model 3MLegend, also available from the Fox Valve Development Corporation. Theair-entrained supply stream 82 of discrete particles is carried by aconduit 97 to a particle carrying conduit comprising the particledelivery chute 94 and the mask delivery nozzle 120. The chute 94 directsthe supply stream 82 of particles to the mask delivery nozzle 120.

The conduit 97 can have a circular cross-section with an inner diameterof about 6.0 cm (2.4 in.) and can include bends 98 and 99 having aradius at the center of the duct cross-section of at least about 30 cm(12 in.). The bends 98, 99 and the particle delivery chute 94 preferablylie in a common plane, which common plane is parallel to the plane ofFIG. 4 and passes through the center of the forming cavities 44. Thebends 98, 99 help to center the particles in the conduit 97 in thiscommon plane. Positioning the bends 98, 99 and the chute 94 in thiscommon plane aids in aligning the first intermittent stream 103 ofparticles passing through the mask 100 within the forming cavities 44.

The embodiment shown in FIG. 4 provides a metered quantity of discreteparticles, combines the metered quantity of discrete particles with thesecond intermittent stream 105 of discrete particles deflected by themask, entrains the combined metered and deflected discrete particles inan air flow to form an air-entrained supply stream 82, and directs theair-entrained supply stream 82 of discrete particles to form an acuteincluded angle A with the mask 100.

The embodiment shown in FIG. 4 is advantageous in that it does notrequire the two mode operation of FIG. 3. The embodiment shown in FIG. 4is also advantageous because the discrete particles deflected by themask 100 for recycling are continuously mixed with freshly metereddiscrete particles from the metering device 80. Such an arrangementprovides recycling of the discrete particles which is independent fromthe supply source (not shown) of the discrete particles. Therefore, theembodiment shown in FIG. 4 can be easily adapted to different productionsites having different types or arrangements of supply sources of thediscrete particles.

In one embodiment of the present invention, the air-entrained stream offibers 62 can comprise about 1 to about 24 kg/minute of fiber carried inan air stream having a velocity of about 610 meter/minute (2,000feet/minute) to about 4,600 meter/minute (15,000 feet/minute) and an airflow rate of about 3.8 cubic meters/minute (136 cubic feet/minute) toabout 29 cubic meters/minute (1,020 cubic feet/minute). Theair-entrained stream of particles 82 can comprise about 1 kg/minute toabout 20 kg/minute of particles carried in an airstream having avelocity of about 610 meter/minute (2,000 feet/minute) to about 3,700meter/minute (12,000 feet/minute) and an air flow rate of about 1.7cubic meters/minute (60 cubic feet/minute) to about 10.2 cubicmeters/minute (360 cubic feet/minute).

FIG. 5 is a cross-sectional side view of the mask 100 and the maskdelivery nozzle 120. The mask 100 is shown disposed within an enclosure140. FIG. 6 is a front elevation view of the enclosure 140 taken alongline 6--6 in FIG. 5, with the enclosure 140 partially cut-away. FIGS. 7and 9 show different embodiments of the mask 100.

Referring back to FIG. 5, the mask delivery nozzle 120 can be anextension of the particle delivery chute 94. The mask delivery nozzle120 directs the air-entrained supply stream 82 of discrete particles toform an acute included angle A with the diverting surface 110. The term"acute angle" refers to an angle less than ninety (90) degrees. Theangle A is measured from the imaginary axis 83 along which theair-entrained stream of discrete particles 82 is directed, rather thanfrom the surface of the supply stream 82, which may diverge or convergeslightly with respect to the axis 83 of the stream 82. If the axis 83 iscurved, the angle A is measured from the tangent of the axis 83 wherethe axis 83 intersects the plane of the diverting surface 110.

Referring to FIGS. 5 and 6, the mask 100 is preferably supported forrotation in a cavity 143 within an enclosure 140. The enclosure 140isolates the mask 100 and the particle streams 82, 103, and 105 fromsurrounding conditions which might otherwise adversely affect theformation of the particle stream 103. In particular, the cavity 143 inthe enclosure 140 is closed to surrounding atmospheric conditions tomaintain the air flows which carry particle streams 82, 103, and 105.The enclosure 140 also serves as a containment structure for holdingparticle dust.

The enclosure 140 includes an upstream wall 150, a downstream wall 160,a top wall 155, and side walls 157, 159. A trough 408 can be joined tothe bottom of the enclosure 140 for receiving particles deflected by thediverting surface 110. The trough 408 can include one or more vents 409for providing an air passage into the trough 408 and the conduit 410.Such an air passage provides air for carrying particles in the conduit410.

The upstream and downstream wall 150 and 160 are parallel to and closelyspaced from the mask 100. The spacing between the upstream wall 150 andthe mask 100 is preferably about 1.1 cm (0.43 inch). The spacing betweenthe downstream wall 160 and the mask 100 is preferably no more thanabout 0.3 cm (0.12 inch). The spacing between the upstream wall 150 andthe mask 100 is greater than the spacing between the downstream wall 160and the mask 100 in order to provide a flow path for the deflectedintermittent stream 105 of discrete particles.

The mask delivery nozzle 120 extends through an aperture 152 in theupstream wall 150. The delivery nozzle 120 can have an elongatedinternal passage 124 oriented radially from the axis 101 of the mark100. The elongated passage 124 can have a height D of about 1.7 cm (0.69inch) and a width W (FIG. 6) of about 9.4 cm (3.7 inch). The deliverynozzle 120 has a beveled face 122 parallel to the mask 100 andpositioned intermediate the upstream wall 150 and the mask 100 toprovide close spacing of the nozzle 120 from the diverting surface 110.The beveled face 122 is preferably spaced a distance 123 from the mask100 of about 0.8 cm (0.3 inch) to precisely direct the air-entrainedsupply stream 82 of discrete particle against the diverting surface 110.

The downstream wall 160 includes a downstream passageway 162 forreceiving the first intermittent stream 103 of particles passing throughthe mask. The passageway 162 can converge in the downstream directionfrom an upstream entrance enlarged with respect to the internalpassageway 124, as shown in FIG. 5. The enlarged upstream entrance ofthe passageway 162 aids in capturing all particles passing through themask 100.

An adapter 170 joins the downstream wall 160 to the diverging duct 65. Apassageway 172 extending through the adapter 170 provides a flowpaththrough which the first intermittent stream 103 of discrete particlesenters the diverging duct 65. In a preferred embodiment the axis 119 ofthe first intermittent stream 103 of particles forms an angle G of about10 degrees to about 50 degrees with the air-entrained stream of fibers62, and most preferably about 24 degrees.

FIG. 8 shows a longitudinal distribution of absorbent gelling materialparticles in an absorbent core, as measured along the longitudinal axis21 of the diaper 20 shown in FIG. 1. The distribution includes arelatively high basis weight region 1003, a relatively low basis weightregion 1002, and transition regions T between the high and low basisweight regions 1002 and 1003. As the mask 100 rotates about axis 101,the air-entrained supply stream 82 of particles is intermittentlyinterrupted by the diverting surface 110 and split into the first andsecond intermittent streams 103 and 105.

In one embodiment the mask 100 can rotate once for each fibrous web 41formed on drum 42, in which case, the distribution shown in FIG. 8corresponds to the distribution of absorbent particles along the lengthof one shaped core component 34. In other embodiments it may bedesirable to rotate the mask 100 more or less than one revolution foreach fibrous web 41 formed on drum 42.

As shown in FIG. 7, the diverting surface 110 can comprise a circularsector, such as a sector of a disk. The diverting surface 110 cansubtend an angle B from a leading edge 111 to a trailing edge 113. Therelatively high basis weight region 1003 corresponds to those angularpositions of the mask 100 where relatively little, or none, of thesupply stream 82 of discrete particles is deflected by the divertingsurface 110. The relatively low basis weight region 1002 corresponds tothose angular positions of the mask 100 where a relatively largepercentage, or all, of the stream of particles 82 is deflected by thediverting surface 110. The transition regions T correspond to thoseangular positions of the mask 100 where the leading and trailing edges111 and 113 intersect the supply stream 82 of particles.

The mask 100 is supported for continuous motion with respect to theair-entrained stream of particles 82 to avoid the inertial forces anddesign and control complexities associated with an apparatus thataccelerates and decelerates between two stationary positions. In apreferred embodiment of the present invention, the mask 100 is supportedfor continuous rotation about the axis 101. In one preferred embodiment,the mask 100 is fixed to shaft 102, and shaft 102 is rotatably supportedon bearings (not shown). The mask 100 is preferably rotated at asubstantially constant angular velocity to avoid inertial forcesassociated with angular acceleration and deceleration. By a"substantially constant angular velocity" it is meant that the mask 100is rotated to maintain an angular velocity of within about 2 percent ofa baseline angular velocity, with it being understood that therotational speed of the mask 100 may be temporarily increased ordecreased by no more than about 2 percent of the baseline angularvelocity in order to maintain a desired phasing of the angular positionof the mask 100 with the angular position of the foraminous forming drum42.

In an alternative embodiment (not shown), the mask 100 can comprise anendless belt having an apertured surface. The endless belt can be drivenby a motor or other driving means at a generally constant speed, and theparticle nozzle 120 can direct the air-entrained stream 82 of discreteparticles to form an acute included angle A with the belt surface. Theapertured belt surface splits the air-entrained supply stream 82 ofdiscrete particles into the first stream 103 passing through theapertures in the belt surface, and the second stream 105 deflected bythe belt surface.

Applicants have found that directing the air-entrained stream ofdiscrete particles 82 to form an acute included angle A with thediverting surface 110 provides benefits with respect to pulsing andrecycling the discrete particles. A supply stream 82 of particlesdirected normal to the diverting surface 110 could be reflectedbackward, into the incoming particle stream 82. Such reflected particlescould disrupt the incoming particle stream, thereby increasing thetransition regions T, or otherwise complicating the formation of a welldefined intermittent stream of particles passing through the mask 100.Such a well defined intermittent stream is desirable to provide distincthigh and low basis weight regions 1003 and 1002. In addition, suchbackward reflected particles can be scattered in random directions,thereby complicating recycling of the discrete particles deflected bythe diverting surface 110.

According to the present invention, when the supply stream 82 ofdiscrete particles is directed to form an acute included angle A withthe diverting surface 110, the deflected particles in the secondintermittent stream 105 will have a component of momentum parallel tothe diverting surface 110. This component of momentum parallel to thediverting surface will carry the deflected particles to a predeterminedlocation. Referring to FIG. 5, the momentum of the deflected particlesin the first intermittent stream 105 carries the deflected particles toa trough 408 connected to the bottom of the enclosure 140. The trough408 is joined to the conduit 410 to provide a flow path for recycling ofthe deflected particles.

As the angle A is decreased, the component of momentum of the particlesparallel to the diverting surface 110 will increase. The angle A ispreferably less than about sixty degrees, and more preferably less thanabout 45 degrees to provide a relatively large component of particlemomentum parallel to the diverting surface 110. However, without beinglimited by theory, it is believed that the angle A should be at leastabout 20 degrees, and can be about 24 degrees to be generally equal tothe angle G. Referring to FIGS. 5 and 6, the depth D of the internalpassageway 124 has a projected height H on the diverting surface 110which is approximately equal to the depth D divided by the sine of angleA. For a fixed depth D, the projected height H will increase as theangle A is decreased, resulting in a longer transition region T in FIG.8. In one embodiment of the present invention, the angle A can bebetween about 20 to about 30 degrees to provide an adequate component ofparticle momentum parallel to the diverting surface 110 without creatingan unacceptably long transition region T.

Referring to FIG. 6, a portion of the downstream wall 160 of theenclosure 140 is cutaway to show the mask 100 supported for rotation onthe shaft 102. FIG. 6 shows the mask 100 in a position corresponding toa transition region T, with the trailing edge 113 intersecting thesupply stream 82 of discrete particles. It is generally desirable todecrease the longitudinal length of the transition region T in order toprovide more precise placement of the absorbent gelling material in theabsorbent core. The longitudinal length of the transition region Tdecreases with increasing radial offset S of the internal passageway 124from the axis 101 of the mask 100. The transition region T increaseswith increasing depth D and with decreasing included angle A. For a maskrotational speed of about 600 RPM, an angle A between about 20 and 40degrees, and the width W and depth D listed above, the offset S can beabout 4.8 cm (1.9 inch) to provide an acceptable transition region T ofabout 42 degrees of rotation of the mask 100, or about 12 percent of thetotal longitudinal distribution shown in FIG. 8 corresponding to onerotation of the mask 100.

The nozzle 120 directs the supply stream 82 to have a velocity componentout of the plane of FIG. 6, and a velocity component directed verticallydownward. The mask rotates clockwise in FIG. 6, as viewed from thedownstream side of the mask, and has a vertically downward velocitycomponent 117 as it intersects the supply stream 82. It is desirable torotate the mask 100 such that the mask 100 intersects the supply stream82 with a velocity component 117 parallel to a velocity component of thesupply stream 82. Parallel motion of the mask 100 with a velocitycomponent of the supply stream 82 reduces the chance that the leadingedge 111 or the diverting surface 110 will reflect particles backwardinto the incoming particle stream 82.

Referring again to FIG. 7, the diverting surface 110 can have one ormore apertures, such as circumferentially extending slots 115. The slots115 can be radially spaced apart and radially aligned as shown in FIG.7. Two apertures are considered to be radially aligned if a radial linedrawn through the axis 101 intersects both apertures. The radiallyspaced apart and radially aligned circumferentially extending slots 115shown in FIG. 7 provide a particle distribution in the low basis weightregion 1002 which is generally uniform in the lateral direction(parallel to the lateral centerline 23 of the diaper 20), and which hasa basis weight greater than or equal to zero and less than the basisweight in the relatively high basis weight region 1003.

FIG. 9 shows an embodiment of the mask 100 in which the radial width ofradially spaced apart and radially aligned apertures, such as thecircumferential slots 115A, 115B, and 115C, varies as a function ofradial position of the slots 115. Such a variation in radial width ofthe slots 115 can provide a lateral distribution of particles in thecore perpendicular to the longitudinal axis 21. Such a lateral variationis shown in FIG. 11. For instance, the variation in radial width shownin FIG. 9 can provide a lateral particle distribution having arelatively high basis weight region 1013 along the longitudinalcenterline 21 of the diaper 20 and relatively low basis weight regions1012 laterally outward of the region 1013. Each slot 115 can have aconstant radial width, or alternatively, one or more of the slots 115can have a variable radial width. In an alternative embodiment, circularapertures having a diameter that varies as a function of radius can beused to provide a lateral variation in basis weight. Of course, otheraperture shapes can also be used.

In an alternative embodiment (not shown), the diverting surface 110 cancomprise an uninterrupted surface having no apertures for providing aregion 1002 having no absorbent gelling material. In yet anotherembodiment the diverting surface 110 can extend through 360 degrees andinclude a circumferentially varying pattern of apertures for providingtwo or more regions of different basis weight in the longitudinaldirection. The mask 100 can be formed from any suitable material whichcan resist abrasion, including, but not limited to stainless steel.

In the embodiment shown in FIG. 5, the particle nozzle 120 directs theair-entrained stream of particles 82 with a vertically downward velocitycomponent. In addition, the diverting surface 110 may be inclined withrespect to the horizontal plane and may rotate about an axis 101inclined with respect to the vertical axis. As shown in FIG. 5, the axisof rotation 101 of the mask 100 can be horizontal, and the divertingsurface 110 can be vertical. Such an arrangement has the advantage thatgravity assists in directing the deflected particles in the secondintermittent particle stream 105 into the trough 408 and the conduit410.

FIG. 10 schematically illustrates a means for maintaining a desiredphasing of the angular position of the mask 100 with the angularposition of the foraminous forming drum 42 in order to maintain thedesired longitudinal distribution of absorbent gelling material in theabsorbent pads formed on the forming drum 42. The means for maintainingthe desired phasing includes a master position resolver 502, a slaveposition resolver 504, a computer 510, and a motor controller 530.

The mask 100 is driven directly, or indirectly, by a motor 104 through adrive train which includes the shaft 102. The motor 104 can be abrushless DC electric motor such as is available from the RelianceElectric Company of Cleveland, Ohio. Forming drum 42 is driven directlyor indirectly by a motor 45 through a drive train which includes shaft47. The master position resolver 502 detects the angular position ofshaft 47, or a shaft geared to shaft 47, as indicated by connection 501.The master resolver 502 provides a signal representing the position ofshaft 47 to the computer 510 via data line 506. The slave positionresolver 504 detects the angular position of the shaft 102, or a shaftgeared to the shaft 102, as indicated by connection 526. The slaveposition resolver 504 provides a signal representing the position ofshaft 102 to the computer 510 via data line 522. Using the input signalsfrom data lines 506 and 522, the computer 210 determines and sends aproportionate analog voltage signal to the motor controller 530 via thedata line 528. The motor controller 530 provides a speed signal to themotor 104 via data line 532 in order to speed or slow the motor 104 asneeded to maintain the angular position of the mask 100 phased withrespect to the angular position of the forming drum 42.

In one embodiment, the mask 100 makes one revolution for each absorbentcore, or five rotations for each rotation of a forming drum 42 havingfive forming cavities 44. Both the master and the slave resolvers 502and 504 are assigned 4096 counts per revolution. The computer 510compares the number of counts received from each of the resolvers in agiven time period to determine a position error of the mask 100 relativeto the forming drum 42.

Suitable master and slave position resolvers 502 and 504 are availablefrom the Reliance Electric Company of Cleveland, Ohio under the modeldesignation 57C360 or 57C361. A suitable computer 510 is available fromthe Reliance Electric Company under the name Reliance AUTOMAX DCS(distributed control system), and includes a power supply 512, aReliance Model 7010 CPU 514, a master resolver card 516, a slaveresolver card 518, and an analog output card 520. A suitable motorcontroller 530 is a Reliance Model HR2000 motor controller set to "speedmode." The computer 510 can be configured and programmed according tothe AUTOMAX Programming Reference Manual, Version 2.0; the AUTOMAXSystem Operation Manual, Version 3.0; and the AUTOMAX Hardware ReferenceManual. In an alternative embodiment, the mask 100 and the forming drum42 can be coupled mechanically to maintain the desired angular phasing,such as with a timing belt, timing chain, or gear train.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope of the invention. For instance, in theembodiments shown, the particles in one of the intermittent streams 103,105 are directed to a web, and the particles in the other stream arerecycled. Alternatively, the particles in both intermittent streams canbe directed for laydown on different webs, or on different portions ofthe same web. It is intended to cover, in the appended claims, all suchmodifications and intended uses.

What is claimed is:
 1. A method for forming an intermittent stream ofdiscrete particles for application to a fibrous web, the methodcomprising the steps of:forming a supply stream of the discreteparticles, wherein at least some of the discrete particles comprise anabsorbent gelling material; continuously moving a mask having adiverting surface relative to the stream of discrete particles; anddirecting the supply stream of discrete particles to form an acuteincluded angle with the diverting surface and splitting the supplystream of discrete particles into a first intermittent stream passingthrough the mask and a second intermittent stream deflected by thediverting surface.
 2. The method of claim 1 comprising the step ofdirecting discrete particles in one of the intermittent streams to applya nonuniform distribution of discrete particles to the fibrous web.
 3. Amethod for applying discrete particles to a fibrous web, the methodcomprising the steps of:supporting the fibrous web; conveying thefibrous web; providing a supply stream of discrete particles, wherein atleast some of the discrete particles comprise an absorbent gellingmaterial; supporting a mask having a diverting surface for continuousrotation about an axis; continuously rotating the mask about the axis;directing the supply stream of discrete particles to form an acuteincluded angle with the diverting surface and splitting the supplystream of discrete particles into a first intermittent stream ofparticles passing through the mask and a second intermittent stream ofparticles deflected by the diverting surface; and directing the discreteparticles in one of the intermittent streams to the fibrous web.
 4. Amethod for forming airlaid fibrous webs having discrete particles, themethod comprising the steps of:providing an airlaying means having aforaminous forming element for forming an airlaid fibrous web; providingan air-entrained stream of fibers; providing an air-entrained supplystream of discrete particles; supporting a mask for continuous rotationof a diverting surface about an axis; continuously rotating the maskabout the axis; directing the supply stream of discrete particles toform an acute included angle with the diverting surface for splittingthe supply stream of discrete particles into a first intermittent streamof particles passing through the mask and a second intermittent streamof particles deflected by the diverting surface; combining theair-entrained stream of fibers with one of the intermittent streams ofparticles to form a combined stream comprising an intermittent stream ofparticles within a continuous stream of fibers; and directing thecombined stream of fibers and particles to the forming element of theairlaying means.
 5. The method of claims 3 or 4 wherein the supplystream of discrete particles is directed to form an included angle ofless than 60 degrees with the diverting surface.
 6. The method of claim5 wherein the supply stream of discrete particles is directed to form anincluded angle of about 20 to about 30 degrees with the divertingsurface.
 7. The method of claims 3 or 4 further comprising the step ofphasing the position of the mask with the position of the web.
 8. Themethod of claims 3 or 4 including the step of inclining the divertingsurface with respect to the horizontal axis.
 9. The method of claim 8wherein the step of directing the supply stream of discrete particles toform an acute included angle with the diverting surface comprisesdirecting the supply stream of discrete particles with a verticallydownward velocity component.
 10. The method of claim 4 comprising thestep of combining the air-entrained supply stream of fibers with thefirst intermittent stream of particles passing through the mask.
 11. Themethod of claim 4 wherein the step of providing an air-entrained supplystream of discrete particles comprises:providing a metered quantity ofdiscrete particles; combining the metered quantity of discrete particleswith the second intermittent stream of discrete particles deflected bythe mask; and entraining the combined metered and deflected particles inan airflow to form an air-entrained supply stream of discrete particles.12. The method of claim 4 wherein the step of providing an air-entrainedsupply stream of discrete particles comprises providing an air-entrainedsupply stream of discrete particles wherein at least some of thediscrete particles comprise an absorbent gelling material.
 13. Themethod of claim 3 comprising the step of directing discrete particles inone of the intermittent streams to apply a nonuniform distribution ofdiscrete particles to the fibrous web.
 14. The method of claim 4comprising the step of directing discrete particles in one of theintermittent streams to apply a nonuniform distribution of discreteparticles to the fibrous web.